Flame heating metal material to lower the yield strength so that the shape of the stock can be changed is well known in the art. Flame heating is commonly used in processes associated with the bending and forging of metal stock and in heat treating applications.
Forming of a thickened linear edge along an edge of a cold metal plate or sheet stock is a common practice. An example of this is shown in U.S. Pat. Nos. 1,040,398, to C. L. Parmelee, dated Oct. 8, 1912 and 3,400,566 to, W. Gauer, dated Sep. 10, 1968. Each patent discloses a plurality of rollers for forcibly engaging the cold metal stock and forming a thickened edge along the full length of the linear edge. Forming a thickened edge by displacing cold material places extremely high loads on the rollers which causes premature roller wear. This wear causes deviations in the shape of the formed edge and results in a high incidence of scrap of the resulting formed material. These excessively high loads are also transferred to other parts of the machine forming the stock causing premature wear and failure of these parts. In addition, special materials and heat treated materials cannot be cold rolled without cracking.
Several passes between the forming roller and stock is required to produce a thickened edge along the cold edge of the stock. Since the quality (surface finish, shape and accuracy) of the formed thickened edge is inversely proportional to the magnitude of force applied to the forming rollers it is advantageous to reduce the force and increase the number of passes. It has been found that high forces tend to cause the metal to push and tear in the direction of movement which results in a reduction in the quality of the final formed product. The large number of passes required to obtain a quality edge also increases the cost of manufacture and causes a reduction in the output.
Forming cold metal work hardens the material which may not be a desirable in metal plate having a formed edge. Mill scale (iron oxide) often found on the surface of metal plate flakes during cold forming which causes abrasion of the forming roller and causes premature roller wear. Heating of the metal plate causes the mill scale to pop off which reduces the mill scale abrasion problem. The ultimate tensile and yield strength of the plate edge being formed is reduced by heating and therefor the problems associated with cold forming are eliminated. It would be advantageous to provide an apparatus capable of controllably heating the metal plate during forming to eliminate these cold forming problems. However, the forming of irregular shaped edges, intermittent formed edges, or raised edges adds a dynamic dimension to the forming process not addressed by conventional devices.
Selective forming of a thickened edge along an edge of a metal plate is disclosed in U.S. Pat. Nos. 5,024,074, dated Jun. 18, 1992, and U.S. Pat. No. 5,113,677, dated May 19, 1992, both to D. L. Blunier et al. and assigned to the Assignee of the instant invention. Selective forming refers to the ability to upset either continuous or intermittent thickened edges on a plate having linear or irregular shaped edges. An apparatus capable of selective forming is subjected to variable forces, for example, caused by the forming of an intermittent thickened edge along a plate having a straight edge, and a thickened edge, intermittent or otherwise, along a plate edge having an irregular shape. These variable forces increase in magnitude in response to, for example, an increase in plate thickness, material hardness, feed speed of the plate relative to the forming apparatus and the like. As indicated above it is advantageous to reduce the force--speed ratio in some manner so as to maximize productivity, improve quality, and reduce cost.
U.S. Pat. No. 1,891.338, to Lester W. Snell, dated Dec. 20, 1932 discloses a fixed flame burner disposed adjacent a tube bending die for the purpose of heating the tube during bending. This heating of the tube is localized and causes upsetting of the tube during bending so that the crossectional thickness of the tube is controlled from thinning at the bend. This fixed burner is suitable for use in the bending of a single tube size but it is not appropriate for use in bending tubes of other diameters and thickness since the heating locations are fixed and do not provide an ability to adjust for varying tube sizes, shapes, and thickness.
Because metal plates requiring edge forming vary in thickness, configuration, edge profile, shape, material and the like, a fixed flame heating device such as disclosed in this patent is not suitable for plate edge forming. Further, in order to accommodate these differences it is necessary to provide an apparatus with variable heat and plate edge following capabilities.
The present invention is directed to overcoming one or more of the problems as set forth above.